Conventionally, as liquid pressure devices of these kinds, a damper interposed between a vehicle body and a truck of a railway vehicle, and suppresses vibration of the vehicle body in a right and left direction with respect to a vehicle traveling direction is known, for example, as illustrated in JP 2000-238637 A.
To be specific, the damper includes a cylinder connected to one of the truck and the vehicle body of the railway vehicle, a piston inserted into the cylinder in a freely slidable manner, a rod inserted into the cylinder, and connected to the piston, and the other of the truck and the vehicle body, a rod-side chamber and a piston-side chamber divided in the cylinder with the piston, a tank, a first on-off valve provided in the middle of a first passage that allows the rod-side chamber and the piston-side chamber to communicate with each other, a second on-off valve provided in the middle of a second passage that allows the piston-side chamber and the tank to communicate with each other, a discharge passage connecting the rod-side chamber to the tank, and a variable relief valve provided in the middle of the discharge passage.
In the damper configured in this way, damping force generated at the time of expansion/contraction can be adjusted with the variable relief valve. Further, when the first on-off valve is opened and the second on-off valve is closed, the expansion-side chamber and the contraction-side chamber communicate with each other, hydraulic oil is not pushed from the cylinder to the discharge passage at the time of expansion, and the damper does not exert the damping force at the expansion side although the damper can exert the damping force at the contraction side.
Further, when the first on-off valve is closed and the second on-off valve is opened, the contraction-side chamber and the tank communicate with each other, the hydraulic oil is not pushed from the cylinder to the discharge passage at the time of contraction, and the damper cannot exert the damping force at the contraction side although the damper can exert the damping force at the expansion side. If the damper is configured in this way, the damper can be set to be so-called one-side effective by opening/closing of the first on-off valve and the second on-off valve, and the damper does not automatically generate the damping force in a region where skyhook control force is unable to be generated. Therefore, the vehicle body of the railway vehicle can be easily semi-actively controlled.